1. Field of the Invention
The present invention relates to a silver halide photographic emulsion.
2. Description of the Related Art
U.S. Pat. No. 3,297,446 discloses a photographic silver halide emulsion sensitized by at least two different sensitizers, i.e., a noble metal sensitizer and an labile selenium sensitizer. A gold sensitizer, a platinum sensitizer and a palladium sensitizer are exemplified as the noble metal sensitizer, and the use amount of the palladium sensitizer is about 10.sup.-6 mol per mol of silver.
JP-B-52-34492 ("JP-B-" means Examined Published Japanese Patent Application) discloses a silver halide photographic emulsion preparation method characterized in that a silver potential is set to be 100 mV or more and/or the pH is set to be 7.5 or more upon addition of a noble metal sensitizer and a non-labile selenium compound, thereby performing sensitization. A gold sensitizer, a platinum sensitizer, and a palladium sensitizer are exemplified as the noble metal sensitizer, and the amount of the palladium sensitizer used is about 10.sup.-6 mol per mol of silver.
Each of JP-B-52-34491, JP-B-53-295, JP-B-52-36009, JP B-52-38408, and JP-A-60-151637 ("JP-A-" means Unexamined Published Japanese Patent Application) discloses a method for performing sensitization by using a noble metal sensitizer and a selenium sensitizer or an emulsion sensitized by the method. In each application, the use amount of a palladium sensitizer as the noble metal sensitizer is about 10.sup.-6 mol per mol of silver.
However, the above described emulsions or emulsions obtained by the above described methods have not enough sensitivity and are unstable.